1) Field of the Invention
The invention herein relates to film thickness control in coating systems, specifically a dynamic film thickness control system/method and its utilization.
2) Description of the Prior Art
Due to significant technological progress in recent years, the requirements of uniform film thickness have become considerably stringent. For example, the film currently utilized on aircraft cockpits to reflect electromagnetic waves is a single layer transparent, conductive oxide film such as indium-tin oxide or indium-zinc oxide film. The precision requirements of which are not great; however, these will be further improved into higher precision multi-layer optical films in the future as technology advances.
Referring to FIG. 1, an example conventional coating system is comprised of an optical thickness monitoring light source assembly 1 (referred to hereafter as the light source), an optical control test glass 2 (referred to hereafter as the test glass), an optical control detector 3 (referred to hereafter as the detector), a first window 4, a second window 5, a third window 6, a substrate placement fixture 7, a substrate 8 to be coated, a quartz crystal and its placement fixture 9 (referred to hereafter as the quartz crystal), and a vapor source 10, wherein the light ray path is composed of a projected ray 11, a penetrating ray 12, and a reflected ray 13; the coating material evaporated from the vapor source 10 deposits to surface of the substrate 8, while also depositing to the surfaces of the optical test glass 2 and the quartz crystal 9; the detector 3 ascertains the changing in the penetrating ratio and/or the reflection ratio to control film thickness and the quartz crystal 9 ascertains changing in oscillating frequency to control film thickness; and the said optical test glass 2 and the quartz crystal 9 are situated at the center of the substrate placement fixture 7. Conventional film thickness control can be by means of optical control or quartz crystal control, or both, with the said optical control device comprised of a light source, a detector, and an optical test glass. To enable uniform film thickness, the said substrate plate placement fixture 7 can be rotated around its own axis (as indicated in FIG. 2) or set into planetary rotation (as indicated in FIG. 3).
When it is set into planetary rotation, the substrate placement fixture 7 not only rotates around the axis of the coating system, but also around its own axis.
Adjusting the height of the film thickness control test glass (the optical test glass 2 and/or the quartz crystal 9) and the height of the substrate placement fixture 7 enables the film thickness of the test glass and the film thickness of the substrate to be of a specific proportion to thereby provide for real-time control over the thickness of the deposited film during the evaporating process. The said evaporating method is suitable for utilization in optical film designs in which the thickness error requirements are not especially great such as anti-reflection films, highly reflective films, and various ordinary spectroscopic films. However, in the case of optical film designs having extremely high precision thickness error requirements (for example, the narrow band filter for optical fiber communications-use, having a total of about 100 layers, with each layer having an error tolerance of 0.003 percent), its suitability is extremely problematic. Furthermore, if the said substrate is very large in dimension, (for example, two to three meters), utilizing the said coating method would require an extremely large vacuum system and incur production difficulties.
The U.S. Pat. No. 5,156,727 (Film Thickness Uniformity Control Apparatus for In-line Sputtering Systems) discloses a design in which a mask plate of variable shape controls film thickness such that following the completion of sputtering, then externally measures the thickness of the film deposited on the substrate and alters the shape of the mask plate to correct subsequent sputtering thickness uniformity based on the measurement results. This method of correcting sputtering thickness uniformity afterwards by changing mask plate shape after sputtering completion is incapable of immediately effecting accurate correction during the sputtering process which, with regard to relatively more complex or high precision requirement optical film designs, would still have production difficulties.
The invention herein is submitted to improve current coating technology by reducing coating thickness errors in optical film designs.